Author
Topic: 24" DIY budget Brick oven progress (Read 23327 times)

We finally (FINALLY!) began some permanent progress on the brick oven.

I started by purchasing high tech insulation for the floor. Everywhere I read sounded like I would severely regret this if I didn't use it. It was $102 for this piece, just enough for a 30"x30" floor.

I picked up about 35 or so bricks from the brick yard, and a 50# bag of heat stop for a total of about $92

At first I bought a masons chisel $9 and thought I could cut bricks this way, but none of the edges were even remotely clean so that idea went into the fire.

I bought 2 abrasive disks to cut bricks, $18, this is without a doubt the least enjoyable part, and I am thinking about renting a wet saw with a diamond bit to do the rest.

I bought a 24" dome styrofoam shape on the internet ($63) that comes in 2 halves.

I was planning on making the first "course" just a layer of bricks on their sides (4" tall) cut up into 3s.

Next I was planning on putting the styrofoam dome on top of bricks (to bring it level with the first course) inside of the oven the dome on top of that, at 12", for a 16" interior height. Now I am pretty sure I will just go for a "perfect dome", 24" inside diameter, 12" inside height. I think for making pizza, this is going to be better than 16". The only problem is that in this case, the first course, which is 4" tall, should have already been angled slightly inwards, or at least should have been much shorter... more like 2.6" (height of brick cut into 3rds) I'd have to slightly compensate for the rest of the layers so it won't be an actual perfect dome... hopefully that will still be ok.

The door width is 14", so I'm expecting to be making 12" pies in it.

It seems like once you get the ball rolling it will come together pretty quickly... hopefully.

I think I will be able to get a good fire going, heat it up very well, then let it go down to embers, push those aside, and fit the pizza in. I will try it without insulating the dome but I'll inevitably be doing that also, which should help a lot.

i didn't really understand how I was supposed to transition from the arch to the opening so I figured I would do the arch first and just work around it. I'll probably have to do some custom cuts around there. The arch was surprisingly easy, whether or not it holds is another story! It was very tight getting the key stone in so hopefully that is a good thing.

The 2 bricks on the second layer on the left are suffering from the problem I expected; since I'm doing a "perfect dome", and the first layer is not angled at all towards the foam dome, the 2nd course needs to be angled more than it would have been otherwise. So I had to shove firebrick shims underneath it otherwise I think I would have had way too much mortar. A little bit sloppy unfortunately but if it holds I don't care.

I am getting closer but wow it is a lot of work. 1 course per day ends up being several hours worth of work by the time I measure and cut the bricks, clean them, prep the previous course, and mortar. I have also learned that I should really wait a full week of watering before firing it up, which I am happy to do to extend the life of the oven and reduce risk of cracking.

i couldnt help but wonder how simple this process would have been if we took this styrofoam dome, created a void for the door opening, and built a box around the entire thing and simply poured refractory mortar. The only problem I see is that you would have thick and thin spots. Thicker in the corners than on the top ans sides, unless you made it in a different shape, more dome like, for example. I am not sure how much that would matter with proper insulation.

I wonder if anyone would like to try this out... or try to do what I am doing or some variation?? I have the other half of my styrofoam dome sitting in a box here that I will never use assuming this one works as planned.

For example, I wonder if it is possible to create two fiberglass shells in the desired shape of the oven. The first would be about three inches smaller all the way around than the second. The larger shell would be placed on top of (i.e., surrounding) the small shell, and refractory concrete would be poured into the void through a hole in the top of the larger shell. The shells could be created with fiberglass by, I believe, pouring a fiberglass mix over a form such as your Styrofoam form or a form made from sand (there would be two such forms, one for the larger, one for the smaller; or, after the smaller shell is made, just add three inches to the smaller form and use it as the larger one). (BTW, how did you create the Styrofoam form---it looks perfect).

Of course, I have not tried this, but hope to when time permits. Creating the two forms might make it possible to more easily build several ovens for friends and family, as they could be brought to the location.

I know this thought is not profound or especially clever, but your post and thought of creating a "surround" reminded me that this is something I hope to try one day.

David, this is a great point... thank you for bringing it up. I always assumed it would vent naturally out the front... and had not really given it much thought. I am sort of winging this whole thing, probably not the best "plan" or lack thereof. Most of these DIY kind of adobe ovens I have seen seem to vent out the front... but now that you've got me reading it sounds like it could make for a very unpleasant experience in loading the oven with either pizza or wood.

I have not closed up the void between the arch and the dome yet, so it would be the right time to add a chimney. Do you have any suggestions? I am not sure I see any reason why I couldn't use a fairly small stove pipe... given the size of the oven.

For example, I wonder if it is possible to create two fiberglass shells in the desired shape of the oven. The first would be about three inches smaller all the way around than the second. The larger shell would be placed on top of (i.e., surrounding) the small shell, and refractory concrete would be poured into the void through a hole in the top of the larger shell. The shells could be created with fiberglass by, I believe, pouring a fiberglass mix over a form such as your Styrofoam form or a form made from sand (there would be two such forms, one for the larger, one for the smaller; or, after the smaller shell is made, just add three inches to the smaller form and use it as the larger one). (BTW, how did you create the Styrofoam form---it looks perfect).

Of course, I have not tried this, but hope to when time permits. Creating the two forms might make it possible to more easily build several ovens for friends and family, as they could be brought to the location.

I know this thought is not profound or especially clever, but your post and thought of creating a "surround" reminded me that this is something I hope to try one day.

Jim

Jim, I got the styrofoam on the internet from "Plasteel". It came as 2 halfs of a 24" circle so I didn't have to cut it or anything... they also carry 30" balls now.

I have the other half of my dome sitting around that I'd be happy to give to someone for the cost of shipping.

I have been warned a few things with the 24" styrofoam dome 1) to not make such a small oven, because I would run into issues with pizza and fire not being able to fit at the same time 2) not to use a solid form on the inside because you can't clean up the joints as you go along. For cost and space restraints I went ahead and did it anyway. I also did not trust myself to make a symmetrical dome otherwise! I think 30" would be great and I probably would have had room for it too. My smallest side of the rectangle platform is something like 35". I wanted to have room for floor + 3" on both sides, then additional room for blanket insulation later.

I think you could use either of these domes for the inside mold. You could probably spray the styrofoam with some sort of release agent so it could be used again also. I am not sure if it would hold up to the weight... but you might put sand underneath the inside layer to give it some extra support. I think you idea would work and it would be very interesting to see it play out!! I would love to see cheaper wood fired ovens for everyone that wants them. I am not sure how many hundreds of pounds of refractory mortar this would require, although for home situations I've heard of people use mixes of regular old cement, lime and some other things readily available.

There do not seem to be many people running ovens between the larger fancy fornobravo ovens and the Earth oven makers. I wanted something permanent that would have excellent heat retention so went my own way.

Thanks for the info, Patrick. Your oven looks really good, and I am sure it will work well and that you will enjoy using it. I also have an oven that is far from perfect, but for the occassional pizza party, it is more than adequate.

Why do these ovens have to be a dome? Why couldn't you simply build a small rectangular brick room?

There are two issues here.

1) Have you ever seen a room on fire? Even with broken windows the room fills up with smoke pretty quickly. Where air flow is involved, aerodynamics is important. You want the relatively colder carbon dioxide to exit the baking chamber as fast as possible (to be replaced by the oxygen a fire needs), and a rounded interior shape helps guide the air to the vent.

2) The pizza often sits at the foci of the parabolic surface so as to maximize absorption of heat reflected from the fire. Heat that's stored then radiated from a perpendicular surface above the pizza is simply a waste of energy. A lot of energy.

The top would be preferable. I don't think you would be happy with a vent sticking out of the side of an oven. The real quandary people often debate is, "Where at the top should it go? The middle, back, or front?" There are too many non-generic design considerations to give a blanket answer to that.

Nice work.In matter to the flue vent, I think that a chimney installed on the front of the oven (landing area) could be more efficient than the one installed in the middle of the dome.There are some relationships that are established along the times. Speaking on dome ovens, the door aperture will be as high as 63% of the higher point of the dome. This is because this is the relationship that assures the best flue of the gases. The fresh air enters by the lower surface of the door; feed the flames, runs on the hearth, climbs the rounded walls and returns to the higher surface of the open, where exits. This path guarantees the higher ratio of burning and heat transference to baked goods and dome hearth, walls and ceiling.If the relationship is lower than 63%, the fresh air divides the entry with the combusted ones. If higher, there will be vortex in the higher surface of the dome, reducing the burning and breaking the flue of hot gases.If the output (chimney) is on the middle of the oven, it is ease to figure that the flue of fresh air will go from the lower and middle surface of the door, heating through the embers and going directly to the exit, wasting hot gases and requiring a lot of combustion to obtain the required temperature conditions.If using a front chimney, could be good to build a landing area or entry, where the chimney will be between the internal oven door and the exit of the landing area.There is a lot of information along the web, to better clarify these points.You could see a lot of pictures and information of my oven (along tons of better ones) on the site www.fornobravo.com . You could search by pizzabrasil (that is me <g>) if you like.Good luck

Thanks for the info on the chimney. I did not think of actually putting the exhaust in front of the arch. I didn't realize how far back it is but I was trying to get the exhaust as close to the front as possible. It is just about touching the rear most part of the arch.

For arch height I went with about 7.5" which is 63% of 12" (interior height).\

I guess we will see how it turns out. I could probably always remove it and try to move it. As you can see I have very little room in front of the oven though!!

Do you think that I would have been better off WITHOUT a chimney in this case? I have seen many ovens that simply vent out of the front? But I was concerned about smoke in my face

P.S. I tried to do a search by username on fornobravo forums but it is saying pizzabrasil is invalid?

Yeah, sorry to came later with this information.A simples idea could be to damp the chimney using a butterfly valve (as simples as a circle of metal sheet with almost the inner diameter of the chimney, moving around a pivot). You could compare the oven temperatures with the chimney opened and dampened.I bet that the chimney will remains closed on baking and opened when going down with the oven temperature (to bake bread after pizzas, as an example).One of the things that I like more is to see the flue of the flames in a white oven. Any bake and I am there to watch that! You will see the path in your oven and this will be the best indication (along with temperature behavior) to you.Venting out by the front is not a problem of smoking your face since the smoke could be noticed. The problems are the infrared flames when in regime. You will never see the eyebrows going out!<g>I use to made temperature strip charts of each one of the fires and the temperature of the flames entering in the chimney was higher than 1000 º C !!!Another word of caution, the position of the chimney is a temptation to be touched; you will need to isolate it.

My fault! Yes, I am not pizzabrasil in fornobravo.com. Is an older site and one of the first that I had visited when thinking oven building. Arevalo53anos it is.

Thanks for all the information. Is there some sort of calculation for flue diameter based on dimensions of the oven? This one is 4" and I was insure if it was necessary to be so large. I know that on a wood burning home oven that puts out 100,000+ BTU, they are usually 6" diameter. I am wondering if I might be able to extend the archway a little bit, and place the chimney into the archway. In this case a slightly smaller diameter pipe may be easier to make work.

Looking at your oven seems easy to extend a lintel in front of the entry of the dome.The lintel, at the end, could be not a structural surface, since the landing area is not (supporting these chimney type). The chimney diameter on the entry (not in the middle, as is) will be 8 to 10 inches, considering that your oven is about 40 inches (estimated diameter of hearth).

I ended up taking out the vent and filling it in. Venting out the front is fine. Ideally yes, I would build the archway longer and stick the vent pipe in the arch. This would also help with wind.

24" is too small. Go 30" at least. 30" I think would be fine to have a good amount of very hot coals and easily fit a small 12" pizza in for 90 second pizzas. You'll never do more than 1 pizza at a time though. But properly insulated, with a small fire around the sides and cook lots of pizza I bet.

My problem is that I left this out in the rain for 9 months, and it ruined my FB Board insulation (underneath the floor). So the top, even with no insulation gets hot and stays pretty hot (it's not losing any heat to conduction) where-as the floor will just not stay hotter than 700F. You can feel the bottom of the 5" concrete slab getting warm below the FB Board.

This was my first pizza on there, that was like 60 seconds I think it could have gone another 30.

Nice work, a great start, I would use an 8X8 terra cotta chimney flue pipe. Probably two lengths to get the smoke and fumes above my breathing area and create decent draft. The opening of the oven should be around 60% of the height of the dome to keep in the heat and let out the smoke. I used Alan Scott and Russell Jeavons books to help me design my oven. It is basically a 3X3ft hearth floor with a tunnel dome above. I used concrete 3/4" wonder-board as a base for my insulated concrete underlayment for the fire brick hearth. This way I didn't have to remove a plywood form. It can be over 1000 degrees F in the oven and you can put your hand on the wonder-board and not feel any warmth. The bricks above are white with that heat.